The present invention relates generally to manual transmissions and, more particularly, to manual transmissions having gearshift locking arrangements.
Unintended disengagement in a manual transmission can result from shift lever inertia forces causing the transmission to disengage from the selected gear position or from a combination of forces both internal to the transmission as well as external. The lever inertia forces usually result from traversing uneven terrain or from power train excitation causing excessive motion of the gear shift lever. Internal forces can be the result of manufacturing deficiencies or unequal load sharing within multi counter shaft units which is a common construction feature of today's heavy duty truck transmissions.
Unintended disengagement can be source of operator irritation, not to mention more serious concerns regarding safe vehicle operation. Over the years various types of locking devices have been employed in attempts to overcome these problems. Such locking devices are usually confined to modifying the jaw clutch components which are used to engage a particular gear to the transmission main or output shaft to produce a locking effect. This can be accomplished by tapering the engaging internal and external teeth to produce a dovetail joint type of connection which results in an axial force between the two which causes them remain engaged. While this is effective, the magnitude of the engaging force is dependent upon the load on the power train. Under heavy loads the engaging force is greater. Under light loads the effectiveness of the engaging force is diminished and therefore cannot always be employed to overcome disengagement problems under all types of conditions. Other types of tooth modifications have been utilized over the years but have met with mixed success or created other problems such as durability or manufacturing issues and for those reasons these solutions are not widely employed.
Attempts have been made to control the shift lever inertia forces but these usually interfere with the ability to shift the transmission resulting from the addition of friction or damping forces which must be overcome when shifting from gear to gear.
It is desirable to provide a gearshift locking arrangement that is simple in construction and that minimizes interferences with use of the gearshift.
In accordance with an aspect of the present invention, a manual transmission with a gearshift locking arrangement comprises a first rail having a first shifter having a first slot between first forward and rear ears of the first shifter, first forward and rear engagement members being provided on the first forward and rear ears of the first shifter, a second rail having a second shifter having a second slot between second forward and rear ears of the second shifter, and a shift lever, an engaging portion of the shift lever being movable between the first slot and the second slot, the shift lever being adapted to move the second rail between a second rail forward and rear position when the engaging portion is in the second slot, the engaging portion being engageable with the first forward engagement member when the second rail is in the second rail forward position and the engaging portion being engageable with the first rear engagement member when the second rail is in the second rail rear position.
In accordance with another aspect of the present invention, a shift rail assembly for a gearshift mechanism comprises a shift rail, and a shifter mounted on the shift rail, the shifter comprising forward and rear ears defining a slot for receiving a portion of a gearshift lever, and forward and rear engagement members on the forward and rear ears for engaging an engagement portion of the gearshift lever.
In accordance with yet another aspect of the present invention, a method of operating a gearshift mechanism comprises moving an engaging portion of a shift lever between a first slot in a first shifter of a first rail, the first slot being disposed between first forward and rear ears of the first shifter, and a second slot in a second shifter of a second rail, the second slot being disposed between second forward and rear ears of the second shifter, using the shift lever, moving the second rail one of forwardly and rearwardly relative to the first rail, and, when the second rail is moved forwardly, engaging with the engaging portion a first forward engagement member provided on the first forward ear of the first shifter and, when the second rail is moved rearwardly, engaging with the engaging portion a first rear engagement member provided on the first rear ear of the first shifter.
In accordance with yet another aspect of the present invention, a manual transmission with a gearshift locking arrangement comprises a rail having a shifter having a slot between forward and rear ears of the shifter, the rail being movable between rail forward and rear positions, forward and rear engagement members disposed at positions corresponding to the rail forward and rear positions, and a shift lever, an engaging portion of the shift lever being adapted to be disposed in the slot, the shift lever being adapted to move the rail between the rail forward and rear position, the engaging portion being engageable with the forward engagement member when the rail is in the rail forward position and the engaging portion being engageable with the rear engagement member when the rail is in the rail rear position.